Arc-gap installation



C. BENNETT ARG GAP INSTALLATION I Filed April 7, 1922 /N VENTORATTORNEYS Patemed sept. 2, 1 92/4. i i l,507,365

NUm'rflazu s'TATl-:s PATENT ormen.

. CHARS E. BENNETT, OEDECATUR, GEORGIA, ASSIGNOR TO BALT MANUFACTURINGCOMPANY, OF ATLANTA, GEORGIA, A CORPORATION OF GEOBGIA.

Ane-GA? NsmALLAmIoN.

Application flled April 7, 1922. Serial NO. 550,425.

To al whom z't may concern: absorbent, While cap-able of receiving an Beit known that I, CHARLES E. BENNE'rr, arc without being pitted, orotherwise oba citizen of the United States of America, jectionablyafl'ect'ed by the play of the residing at Decatur, in the county ofDearc thereon. At the axis of the insulator 5 kalb and, State ofGeorgia, have invented it is cupped to form a seat 11 for the concertainnew and useful Improvements in tact 4.

Arc-Gap Installations, of which the follow- Adjustably mounted on therod 3 .is ,a ing is a specification. condenser plate 12 vwhich may havea My invention relates to arc gap installathreaded hub: 13 working onthe threaded 10'I tions,.,and particularly to a gap. terminal, area ofthe r'od. This plate may be overthe object of' my invention being toprovide weighted at one side by a boss 14.- which' a terminal havingcertain structural. and serves to automatically maintain the platefunctional features of advantage over those by gravity in the positionto which it is i shown in my co-pending applications Serial adjusted byscrewing it on the rod. Prefer- I'5 Jos. 402,569, filed August 10, 1920,patented ably, the plate is o-f less diameter than the January '1, 1924,No. 1,479,693, and 457,638, ring 8, and is also dished to conformsubfiled April 1, 1921. stantially to the concave face of the in- In theaccompanying drawingssulator disc 10 So that it may be Shifted on Fig. 1is a side elevation part-ially in sec'- the rod from a position. closeto the disc 10 20 tion of an arc gap terminal in which my to a pointconsiderably spaced therefrom. invention is -illu'stratively embodied;and It will be noted that the plate may be Fig. 2 is a rear elevationthereof. shifted from one side to the other of the The present terminalis adapted for use plane of the condenser ring 8, and Iis thusl in anarc gap installation of the general adJustable toward and from the gapand 25 type indicated in my copending application from the plate of theopposed cooperating above mentioned, or in any other approterminal oflike construction. priate installations. In such installations An arcinghorn 15 may be formed on the two terminals of like construction are ring8 and is flared away from the arc gap generally employed, between whichan arc to assist in drawing out and breaking any 30 is struck on adischarge through .the gap arc that may be formed between the gapcircuit. Inasmuch as the terminals are .terminals on a discharge throughthe gap alike, and an installation of the type men- Circuit.

tioned is well known in the art, 1t suffices A terminal of thischaracter possesses the for the present purpose to illustrate butimportant characteristic that at a given one of the terminals. spacingof the terminals the gap rating As shown, the terminal is supported .uon may be maintained practically uniform, not

a rod 3, to which a circuit connection (Ihot only under both wet and dryconditions shown) may be established in any suitable of the gap atnormal line voltage, but also fashion. The end of the rod is threaded,under the same conditions when high fre- 40 and the metallic arcingcontact 4 is screwed quency current is imposed on the line. In t-hereon.This contact may be of brass and fact the adjustment of the calibratinis Shaped to present a spherical face toward plate 9 toward and from thegap makes 1t the gap. The hub 5 of the Spider 6 is fixed possible tocreate a condition such that the by a set screw 7 on the rod 3 andcarries are-over at high frequency occurs at lower 13 a condenser ring 8coaxial with the contact4 voltage than is necessary to cause an arc- 4,but spaced outward radially therefrom. over at normal line frequency. InIother Cemented to the inner periphery of the words, the terminals maybe set for dry ring at 9 is a dished insulator disc 10 preconditionunder normal voltage at 60 cycles senting its convex face toward thearcing without danger of discharge at lower o- 50 cont-act 4-that is,toward the gap. The tentials in wet weather, while high gematerial ofwhich the insulator disc is quency disturbances Will span the gap evenmade may be alava, specially prepared before reaching the line 'voltagevalue. porcelain, a suitable clay compound, or By use of speciallyprepared and fired other highly refractory insulating material, porousporcelain, a non-metallic surface is which is porous or moisturepermeable or presented to the rain drops or moisture, 110

which are .instantly Spread or absorbed entirely, preventing ytherete'ntion of -drops of' water in the gap path. They then do not offer apoint for flux concentration or make the gap distance shorter, as is thecase, where all-metal terminals are used. The

importance of 'this characteristic can be appreciated especially withgaps of short spacing, Where the presence-of a drop of water may sodecrease the gap spacing as to cause the gap to break down at a verymuch less potential than that for which it is set, with the consequentunnecessary disturbance of service supplied by the Circuit. Collectionof moisture'in the form of drops, Which arev so often formed on metallicsurfaces' during foggyv or damp weather, even when not rain- 1ng, isimpossible on porous porcelain and the present compensated impulse gapwill,

therefore, not operate at normal line potential due to this cause.

By the use of highly refractory porous porcelain that is not affectedby* the hi-gh temperature of the arc, the pitting and roughening of'thesurface that is always found in metal sphere or horn gaps aftercontinued service, is also avoided, and thegap setting does notchange'its characteristics due to this roughening eflect. With metallicspheres it is not unusual, in short gaps, to find globules of meltedmetal that will represent 10% of the gap setting and reduce the normalbreak down potential by that amount; In the case of large spheres withwide setting, the whole nature of the gap is changed by this rougheningor pitting and instead of presenting a smooth polished surface to thecharge. it soon becomes a series of points whose characteristic breakdown potential for the gap is entirely different from that of theoriginalsphere. This also has a tendency to fix the dischargecontinually at a certain point on the sphere, resulting eventually inactually burning holes through the metal or destroying it en- 'a gapusmg terminals of the present type,

When the porcelain is dry the disoharge area is equal to that of thebrass contact 11 in the center; but when it is wet, the porcelain inefi'ect becomes'a conductor instead of an insulator and thus increasesthe terminal area. In other words, this gap compensates for weatherconditions by this change in electrical characteristics, byautomatically replacing the small' spheres or points 4 with a largespherical area of terminal (4, 8 and 1Q combined) vwith no change inspacing, due to the permeation or absorption" of moisture' by theporcelain disc. These orcelain discs dry out almost immediately a terrain,

vdue to the drying-effect of the electrostatic field always present atthe gap when in service. -While the moisture in the air manifestlydecreases the arc-over voltage value in the usual horn or Sphere gap, itincreases the are-over value of these gaps somewhat, as the larger discof wet porcelain is equivalcnt to and takes on the characteristics of alarge Sphere. Thus, a gap possessing the present terminals, has a higherbreak-down lvalue when wet than when dry,-a most desirable function.

The present compensated impulse gap terminals make it possible to securea gap that has an impulse break-down voltage less than that of ordinarySphere gaps under dry weather conditions. It is on the approach of lastorm, when the gaps are dry, that the greatest stresses are produced onequipment; the insulation being dry, it does not absorb or tend todissipate transient potentials as when all the insulators are wet. Whenwet. the dielectric resistance is lower and it is probable that impulsesdo not rise to the same potential value since there must bev greaterdrainage through the dielectric resistance. v

The potential gradient over insulators. bushings, etc.. is considerablyless per unit of dielectric when wet, and they can stand greater shock.as each unit is not so likely to be subjected to over stressing. It isnecessary, therefore. that a perfect gap should function upon theslightest voltage. ripple,

due to switching surges. induced lightning potentials, static orimpulses of any sort during dry weather conditions. y

The dry weather impulse potential'curve of the present compensatedimpulse gap is considerably lower than' the 60 cycle continuouslyapplied break-down voltage, but can be adjusted in relative value. Thereare two adjustments on the gap, which control the sensitiveness toimpulse voltages. This is accomplished by revolving the adjustingmetallic plates 12. moved closer to the porcelain discs. the sphere gapcharacteristicsundery impulse potentials are obtained and the gap isless sensitive to impulse or high frequency disturbances.

When the plates are close tothe porcelain, the total flux across the gaphas been largely increased because of the greater capacity brought aboutby bringing the two comparatively large metallic plates closer towardWhen these plates are 1 the center of the gap, and as the stress betweenthe faces of the gap due to increased flux density has been increased, aeater impulse potential is required for spar -over. In other words, thedielectric between the electrodes, which includes the porcelain andair,is more uniformly stressed'iand, therefore, requires, as stated above,more potential to overstress or break down the gap.

By revolving the metallic plates away from the rear of the porcelaindisc, I obtain a highly sensitive setting to impulse potentials, since.when the metallic shields are moved back from the porcelain disc, theelectrostatic capacity over the gap, and the flux about the centerpoints has been increased. Therefore, the air around the points becomesmore quickly overstressed, and as a result, a more instantaneous'breakdown occurs and at a lower potential than with the other settingor that of a Sphere.

The moving of the adjusting plates for- Ward and backward from theporous porcelain disc, when wet, does not influence the high frequencyor cycle gap setting, the break-down then following-very nearly thecharacteristics of a large Sphere.

The successful gap and lightning arrester must have little time lag inorder to protect apparatus from harm when subjected to impulsepotentials.

An impulse voltage reflected upon electrical apparatus must have timeand energy in order to rupture insulation. The destructive dischargethrough a dielectric requires not merely a sufiiciently high voltage buta definite amount of energy. The destructive discharge does not occurinstant'ly with its application, but a finite. 'though usually small,time elapses after the application of the voltage before the dischargeoccurs. During this time interval, energy must be supplied to thedielectric. As a result, therefore, the perfect gap and arrestercombinationshould function at the beginning of this energy period inorder to absorb and dissipate disruptive energy and prevent itsenteingthe apparatus to be protected, if possl e.

If this combination has a perceptible time lag, the impulse voltage willbe applied to the dielectric for a part of a time at a given energyrate, and overstressing of the dielectric of the apparatus is sure tooccur. Continual subjectlon to overstressingI will cause injury andultimate breakdown of such appartus.

The present compensated impulse gap terminal fulfills all requirementsof the idea-l gap. It does not change its normal frequency breakdownvalue when wet or dry, and therefore can be given the close dry settinslightlv above normal line potential wit the assurance that it will notdischarge at less than line potential when wet. It does not need-protection by covering, and is set up in free air with nothing torestrict its ventilation. y I

It will discharge impuls'e* or high fre.-

quency disturbances at their inception, giving them the least chance torise to destructive values. Its impulse value and its normal frequencyvalue are Vcapable of calibration independently of each other. Itpref 1. In an arc gap terminal, an arcing contact, an associated dishedinsulator eoaxial therewitli and presenting its convex face to- Ward thegap, in combination with an adjustable condenser plate adapted to liewith- -in the area of the insulator adjacent its concave face.

2. In an arc gap terminal, an arcing contact, -an associated dishedinsulator coaxial tlierewith and presenting its convex face vtoward thegap, in combination with an adjustable condenser plate adapted to lieWithin 'the area of the insulator adjacent its concave face, said platebeing' dished to substantially conform to the curvature of theinsulator;

3. In an arc gap terminal, an arcing contact, a conductor rod leadingthereto, a metallic ring supported by the rod and coaxial with thearcing contact, together with an insulator supported, by the ring andextending between the latter and thearcing contact. I v

4. In an are gap terminal, an arcin contact, an associated insulator, acon enser ring radially spaced by said insulator from the contact, andacondenser plate adjustable across the plane of said ring, toward andfrom the arcing contact.

5. In an arc gap terminal, an arcing contact, an associated insulator, acondenser ring radially spaced by said insulator from the contact, and acondenser plate of less .diameter than the ring and adjustable acrossthe plane of the latter and within the ring, toward and from the arcingcontact.

l l'O 6. In an arc gap terminal, a conductor v rod, an arcing contactatthe end thereof.

a spider mounted on the rod and spaced from said contact, an insulatingdisc supported by the Spider and vsurrounding the arcing contact,together with a condenser vplate adjustably mounted on said rod be-vtween t-he arcing contact and the spider mounting.

7. In an arc gap terminal, a threaded terminal rod, an arcing contact atthe end of said rod, and a condenser plate screwing on said rod toadjust the same toward or from said contact.

8. In an arc gap terminal, a threaded terminal rod, an arcing contact atthe end of said rod, and a condenser plate screwing on said rod toadjust the same toward V or from said contact, together With an in-'sulator interposed'between said condenser 4 kplate and the gap.

cessedto alford'a seat for'the contact.

. 9. In an arc gap terminal, a terminal rod, an arc'ing contact at 'theendl thereof, a

'condenser ring radially spaced from. the contact, a condenser plate,said ring and' plate being electrically connected to the terminal rod",'together With an insulator interposed between said arcing contact andsaid .condenser ring and plate. p

' TO, In an arcv gap terminal, a terminal i rod, anl areing 'contact atthe end thereof, di a eoaxial insulator having a convex an face towardthe contact, said face being reaeomeee 13. In yan arc gap terminal, aconductor rod, an arcing contact at the end thereof, a Spider mounted onthe rod, a condenser ring carried by the Spider and surrounding thearcin contact, together With a condenser 'plate adjustably mounted vonsaid rod be-, 'tween the arcing contact and the spider moiinting.

14. In an arc gap terminal, a conductor rod, an independent arcingcontact Secured at one end to the rod, a moisture-absorbent insulatormounted on the rod and surrounding thel arcing contact, in combinationWith a condenser vmounted on the rod and adjustable toward and from thearcing contact.v

' 15. In. an arc gap terminal, 'a conductor rod, an arcing contact atthe end of the rod, and presenting a curved face toward the gap, incombination with a moistureabsorbent insulator mounted on the rod andperipherally surrounding the gap contact, said insulator presenting acurved face to- Ward the gapythe radius of curvature being difl'erentfrom that of the gap contact.

In testimony Whereof I have signed my name to this s ecification. i

I-IARLES E. BENNETT.

